Cancer Diagnostics
Microscopic evaluation of a tissue section taken from a tumor remains the golden standard for determining a diagnosis of cancer. Analysis of genomic DNA, transcribed genes and expressed proteins all add important information to the histological features detected in the microscope images. Tomorrow's diagnosis, prognostic information and choice of treatment will in all likelihood be based on a synoptic evaluation of morphology in conjunction with analyses of nucleic acids and proteins.
Despite remarkable progress within molecular biology, cancer diagnostics still relies on the use of light microscopy. The development of molecular tools has played an important, although as of yet incremental, role to discriminate a cancer cell from a normal cell. The most commonly used method in addition to histochemical staining of tissue sections is immunohistochemistry which allows the detection of protein expression patterns in tissues and cells using specific antibodies. The use of immunohistochemistry in clinical diagnostics has provided a possibility to not only analyze tissue architecture and cellular morphology, but also to detect immunoreactivity in different cell populations. This has been important to support accurate grading and classification of different primary tumors as well as in the diagnostics of metastases of unknown origin. The most commonly used antibodies in clinical practice today include antibodies against cell type markers, e.g. PSA, MelanA, Thyroglobulin and antibodies recognizing intermediate filaments, CD-antigens etc. and markers of malignant potential, e.g. Ki67, p53, HER-2. All tumor markers, measurable either in serum or from tissue specimens, are generally useful in screening, diagnosis, prognosis or monitoring therapy and/or for early indication of relapse. An ideal tumor marker should have high sensitivity, specificity, and reproducibility, and should be included in a practical, easy, cost-efficient test. Such a marker also should have to predict the prognosis and be useful in patient management. Markers that fulfill all these conditions remain to be discovered.
Prostate Cancer
Prostate cancer (PCa) is the most common cancer in males in developed countries [Stenman et al., 2005; Wilson, 2005]. PCa is the second cause of cancer mortality of men in France (11% of deaths by cancer) [www.doctissimo.fr/html/dossiers/cancer_prostate.htm], it affects 17% of the male population in the United States [Wilson, 2005; Jemal et al., 2008], and surpasses lung as the most frequent cancer site in Italy [AIRT working group, 2006]. The incidence of prostate cancer and the rate of death due to the disease increase exponentially with age [Scardino, 2003]. Due to the increase in the percentage of the old population it is expected that in the United States the number of cases of prostate cancer will increase from 234,000 in 2006 to 380,000 in 2025 [Scardino, 2003].
Early detection is essential for curative prostate cancer therapy and for achieving a decrease in prostate cancer mortality. Unfortunately, the available tests can detect only those cancers large enough to be palpable, visible on ultrasound, or capable of elevating the serum level of prostate-specific antigen (PSA).
Screening is performed with digital rectal examination (DRE) and measurement of serum PSA (prostate specific antigen) level. The latter is the most important biochemical marker for the detection of prostate cancer [Ablin et al., 1970 a, b]. However, the utility of PSA tests is limited by their inability to differentiate cancer from clinically irrelevant, non-malignant conditions (benign prostatic hyperplasia, prostatitis, trauma, and urinary retention) [Stenman et al., 2005; Zhu et al., 2006]. Furthermore, it has been shown that the correlation between PSA and cancer is weaker than initially thought, and PSA is regarded now only as a significant marker for prostate size [Stamey et al., 2004]. Patients who have abnormal DRE findings and/or elevated PSA levels have to be further evaluated with prostate needle biopsy, often guided by transrectal ultrasonography [for review, Akin and Hricak, 2007].
Diagnosis and aggressiveness of the tumor is routinely established by using the Gleason system, which is based exclusively on the architectural pattern of glands of the prostate tumor. This histological method evaluates how effectively the cells of any particular tumor are able to structure themselves into glands resembling of normal, very well differentiated gland architecture. In the Gleason grading system the prostate tumor tissues are classified from grade 1 (very well differentiated) to grade 5 (undifferentiated). The sum of the grades of the two most extended tumor areas gives the Gleason score for each patient, which varies from 2 to 10. Since only a small amount of prostate tissue is obtained by needle biopsy, sampling errors are common. High numbers of biopsy samples from different regions of the prostate are necessary to improve cancer detection and risk assessment [Macchia, 2004; Remzi et al., 2005]. In recent years high throughput techniques such as mass spectrometry and microarray analysis led to the discovery of several transcripts and proteins that are overexpressed in prostate tumors [for review, Bradford et al., 2006]. However, none of them is satisfactory for diagnostic purposes [Bradford et al., 2006].
One of the proteins reported to be expressed in prostate tumors but not in normal prostate is follicle stimulating hormone receptor (FSHR). A polyclonal anti-FSHR antibody, revealed focal expression of FSHR in the basolateral areas of secretory epithelia in human hyperplastic prostate tissue, and focal expression but without cell polarity in adenocarcinomas [Mariani et al., 2006]. In contrast to the data of the present invention, Mariani et al. do not mention any FSHR signal in blood vessels.
Another immunohistochemistry study using a different polyclonal antibody reported strong FSHR staining in cancerous prostate glandular structures, and lower levels of staining in the interstitial cells, but no staining in blood vessels. No staining for FSHR was detected in normal prostate glands [Ben-Josef, 1999]. Moreover, the data are questionable, because the molecular weight of the band detected by their antibodies does not correspond to the known size of FSHR, and could be therefore an unrelated protein which crossreacts with their antibody.
Finally a review [Porter et al 1991] suggests that FSH may affect the pathogenesis and progression of prostate cancer and that altering FSH production may prove to be an active therapeutic approach. However, the authors fail to recognize that targeting FSHR expressed on the epithelial tissue prostate tumor is difficult, because FSHR ligands delivered to the blood cannot cross easily by themselves the endothelial barrier [Vu Hai et al., 2004]. No therapeutic or diagnostic method for targeting prostate tumors is so far available for clinical use. A peptide that binds to prostate tumor microvessels in a strain of transgenic mice has been described in 2002 [Arap et al., 2002]. However, it is not known so far if the peptide is suitable for human diagnostic or therapy.
Radiolabeled antibodies anti-prostate specific membrane antigen (PSMA) have been proposed for diagnostic and therapy of prostate cancer. However, only 16% of patients with prostate adenocarcinoma have positive PSMA immunostaining associated with tumor neovasculature [Chang et al., 1999]. In conclusion there are no validated alternative procedures for specific targeting of prostate tumor vasculature.